“Even when we corrected for known risk factors, we still found a higher rate of both stroke and heart failure in these patients,” lead researcher Dr. Aditi Kalla, a cardiologist at Einstein Medical Center in Philadelphia, told CBS.

Kalla’s study looked at 20 million health records of patients aged 18 to 55 who were discharged from one of more than a thousand hospitals across the United States in 2009 and 2010. Of those patients, 1.5 percent said they’d used marijuana.

Researchers also associated pot with a 26 percent increased risk of stroke and a 10 percent increased risk of heart failure.

“More research will be needed to understand the [reasons] behind this effect,” Kalla said.

The study was not without its detractors

Paul Armentaro, deputy director of the marijuana advocacy group NORML, said the study “is inconsistent with other studies finding no adverse effects to those who consume marijuana.”

Kalla said now that medical or recreational marijuana use is now legal in more than half of U.S. states and a better understanding of pot’s health effects is needed.